1. Field of the Invention
One aspect of the embodiments relates to an image pickup apparatus, and more particularly, to a technique of adding signals.
2. Description of the Related Art
One of techniques to add signals in an image pickup apparatus is disclosed in Japanese Patent Laid-Open No. 2009-033316. In this technique, floating diffusion parts (hereinafter, referred to as FD parts) of pixels adjacent in a vertical direction are electrically connected to each other via an FD-part connection switch. This connection is made for all pixels in a whole effective pixel array area of a solid state image pickup device. Each FD part functions as a part of a charge-voltage conversion unit that converts a transferred electric charge into a voltage.
In the technique disclosed in Japanese Patent Laid-Open No. 2009-033316, when electric charges of three or more FD parts are added together, it is necessary to provide two FD-part connection switches for each FD part to electrically connect the FD part to another FD part at an upper or lower location. This configuration results in an increase in capacitance of the charge-voltage conversion unit. The increase in capacitance of the charge-voltage conversion unit makes it difficult to achieve a high charge-to-voltage conversion factor in converting the electric charge generated in the photoelectric conversion unit into a voltage. In view of the above, one aspect of the embodiments provides an improved technique to add electric charges of FD parts.